Many metal ions (for example, copper, cobalt, silver, manganese, nickel and zinc) are known to have antimicrobial activity. Their modes of action remain unclear but may involve oxidative stress, protein dysfunction of membrane damage in the target cell. Sources of metal ions (for example, metal salts) are often incorporated into oral care formulations to impart antimicrobial properties to the compositions.
Current methods to determine the bioavailability of metal ions in compositions (i.e. the extent to which the metal ions can act at the desired physiological site to bring about the desired clinical or biological effect), rely on measuring the amount of soluble ions in the compositions. Typically in these methods, the compositions are centrifuged to pellet insoluble material, and the amount of a given metal ion in the resulting cleared supernatant is measured to determine the amount of soluble, and thus “bioavailable” metal ions.
However, measuring solubility of metal ions alone may not provide accurate indication of bioavailability. For example, soluble ions may inadvertently be retained in the insoluble fraction following centrifugation and decanting of the supernatant (tzar example, through adsorption onto solids).
It would therefore be desirable to provide an improved method of determining the bioavailability of metal ions which do not rely on solubility alone.